Self-regenerating particulate trap systems for emissions and methods thereof

ABSTRACT

A method and system for treating emissions includes charging particles in an exhaust stream, producing one or more radicals, and oxidizing at least a portion of the charged particles with at least a portion of the produced radicals. At least a portion of the charged particles in the exhaust stream are then attracted on at least one attraction surface which is one of oppositely charged from the charged particles and grounded. The attracted particles are oxidized with another portion of the one or more produced radicals to self regenerate the at least one attraction surface. Downstream from where the attracted particles are oxidized, at least a portion of one or more first compounds in the exhaust stream are converted to one or more second compounds downstream from the attracting. Additionally, at least a portion of any remaining charged particles are oxidized into one or more gases.

This application is a divisional of U.S. patent application Ser. No.11/480,059, filed Jun. 30, 2006, which claims the benefit of U.S.Provisional Patent Application Ser. No. 60/696,978, filed Jul. 6, 2005,which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to emissions treatment systemsand methods thereof and, more particularly, to a self regeneratingparticulate trap system for one or more emissions and methods thereof.

BACKGROUND

There is a growing demand for energy usage in the United States,primarily due to increasing economic activity. This increasing demandfor energy is being met by pursuing increased power generation.Unfortunately, this increase in power generation is resulting in thegeneration of over 160,000 tons of particulate emissions per year in theUnited States polluting the air.

Without significant new controls and treatments of emissions, millionsof individuals will continue to breathe air polluted by theseparticulate emissions. Additionally, these emissions will continue tocause damage to environment in the form of acid rain and smog.Significant reductions in emissions of nitrogen oxides (NOx),particulate matter, nonmethane hydrocarbons, carbon monoxide, sulfurdioxide, and other toxins would result in substantial benefits to boththe public health and the environment.

At the present time a device that is robust, efficient, durable,packagable, and maintenance-free is not available for elimination ofparticulate matter. For diesel engines in particular, several deviceshave been designed to combat the problem of particulate emissions. Mostof these devices use different filtration technologies with eitherthermal regeneration capabilities or manually replaceable filtrationmedia. The problem with these filtration devices is that they quicklyclog and increase the exhaust backpressure thus negatively affectingefficiency and performance. In addition thermal regeneration requiresvast amounts of energy and produces very high temperatures.

As discussed below, other technologies available for separatingparticulate matter from a gas stream have been investigated. Forexample, non-thermal plasma-assisted catalytic reduction of exhaustgases using a corona discharge have been studied and reported in theliterature. J. A. Ekchian, E. N. Balles, D. L. Christeller, J. S.Cowart, and W. D. Fuller, “Use of Non-Thermal Plasma Generated by aCorona Discharge Device to Improve the Efficiency of Three-WayCatalyst”, which is herein incorporated by reference in its entirety,disclosed testing on the use of a corona discharge device for thereduction of HC, CO, and NOx in tailpipe emissions in conjunction with athree-way automotive catalyst and reported significant improvements.

Additionally, M. B. Penetrante, R. M. Brusasco, B. T. Merritt, W. J.Pitz and G. E. Wogtlin, “Feasibility of Plasma Aftertreatment forSimultaneous Control of NOx and Particulates”. SAE Paper 1999-01-3637(1999)”, which is herein incorporated by reference in its entirety,disclosed a study on the feasibility of plasma after treatment of NOxand particulates. This study reported that although NO₂ can be used tonon-thermally oxidize the carbon fraction of particulates, this does notprovide a high level of reduction of NOx since it also leads toconversion of NO to NO₂.

Further, Suzanne E. Thomas, Anthony R. Martin, David Raybone, James T.Shawcross, Ka Lok Ng, Phil Beech, and J. Christopher Whitehead,“Non-Thermal Plasma After Treatment of Particulates-Theoretical Limitsand Impact on Reactor Design”, SAE Paper 2000-01-1926 (2000), which isherein incorporated by reference in its entirety, disclosed work thatwas carried out using non-thermal plasma by introducing packing materialinto the plasma region to increase the residence time for the oxidationof particulate matter in the treatment of diesel exhaust. This referenceshowed that a non-thermal plasma reactor designed in this manner couldbe effective in the oxidation of particulate matter at low temperatures.This reference also reported that a two-stage plasma system might beneeded to convert NO, produced during the process, back to NO₂ upstreamof a catalytic treatment. This reference indicated that the plasma incombination with a catalyst would be required to take care of aldehydesand CO.

Unfortunately, each of the technologies still has one or morelimitations which prevent it from providing a robust, efficient,durable, packagable, and maintenance-free, particulate trap system andmethod.

SUMMARY

A method for treating emissions in accordance with embodiments of thepresent invention includes charging particles in an exhaust stream,producing one or more radicals, oxidizing at least a portion of thecharged particles with at least a portion of the produced radicals. Atleast a portion of the charged particles in the exhaust stream areattracted on at least one attraction surface which is one of oppositelycharged from the charged particles and grounded. The attracted particlesare oxidized with another portion of the one or more produced radicalsto self regenerate the at least one attraction surface.

A system for treating emissions in accordance with other embodiments ofthe present invention includes a housing with a passage having at leastone inlet and at least one outlet, at least one charging system, and atleast one attraction system. The charging system charges particles in anexhaust stream in the passage, produces one or more radicals, andoxidizes at least a portion of the charged particles with at least aportion of the produced radicals. The attraction system attracts atleast a portion of the charged particles in the exhaust stream on atleast one attraction surface which is one of oppositely charged from thecharged particles and grounded in the passage downstream from thecharging system. The attracted particles on the at least one attractionsurface are oxidized with another portion of the one or more producedradicals to self regenerate the attraction surface.

A method for making a system for treating emissions in accordance withother embodiments of the present invention includes providing a housingwith a passage having at least one inlet and at least one outlet,providing at least one charging system, and providing at least oneattraction system in the passage downstream from the charging system.The charging system charges particles in the passage, produces one ormore radicals in an exhaust stream, and oxidizes at least a portion ofthe charged particles with at least a portion of the produced radicals.The attraction system attracts at least a portion of the chargedparticles in the exhaust stream on at least one attraction surface whichis one of oppositely charged from the charged particles and grounded.The attracted particles on the at least one attraction surface areoxidized with another portion of the one or more produced radicals toself regenerate the attraction surface.

A corona discharge device in accordance with embodiments of the presentinvention includes at least one conductive member and a plurality ofteeth along at least one edge of the at least one conductive member. Atleast one electrical connector is coupled to the at least one conductivemember.

A method for making a corona discharge device in accordance with otherembodiments of the present invention includes providing at least oneconductive member and forming a plurality of teeth along at least oneedge of the at least one conductive member. At least one electricalconnector is coupled to the at least one conductive member.

A method of making corona discharge in accordance with other embodimentsof the present invention includes providing at least one conductivemember with a plurality of teeth along at least one edge and couplingthe at least one conductive member to at least one power source. Avoltage from the power source is applied to the at least one conductivemember to generate an ionization discharge.

The present invention provides systems and methods for elimination ofparticulate matter that are robust, efficient, durable, packagable, andmaintenance-free. With the present invention, air quality is improvedthrough significant annual reductions of particulate emissions providingbenefits to public health and the environment. By using non-thermalplasma, the present invention is very efficient in terms of powerconsumption when compared to other prior particle separation andtrapping technologies. Additionally, by self oxidizing carbonparticulates the present invention is able to self regenerate thecatalyzed electrostatic surface. Further, the present invention providesa treatment system which has a lower weigh, and lower system pressuredrop than prior units.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective and partial broken away view of aemissions treatment system in accordance with embodiments of the presentinvention;

FIG. 2 is a perspective view of a corona discharge electrode device inthe emissions treatment system shown in FIG. 1;

FIG. 3 is a side, perspective view of the corona probe for the coronadischarge electrode device shown in FIG. 2;

FIG. 4 is a perspective view of a section of a catalyzed electrostaticsystem in the emission system shown in FIG. 1;

FIG. 5 is graph of experimental test results of particulate matterreduction versus corona discharge voltage;

FIGS. 6A-6C are top, perspective view of other embodiments of coronaprobes for the corona discharge electrode device; and

FIG. 7 is a diagram of test results of particulate matter reduction.

DETAILED DESCRIPTION

An emissions treatment system 10 in accordance with embodiments of thepresent invention is illustrated in FIGS. 1-4. The emissions treatmentsystem 10 includes a housing 12 with a passage 14 having an inlet 16 andoutlet 18, corona discharge electrode devices 20(1)-20(2), a catalyzedelectrostatic system 22, and a catalyst system 24, although theemissions treatment system 10 can comprise other numbers and types ofcomponents in other configurations. The present invention provides anumber of advantages including providing systems and methods forelimination of particulate matter which are robust, efficient, durable,packagable, and maintenance-free.

Referring to FIG. 1, the housing 12 defines the passage 14 which extendsbetween the inlet 16 and the outlet 18, although the housing 12 couldhave other shapes and configurations with other numbers of passages withother numbers of inlets and outlets. The housing 12 has chambers 26(1)and 26(2) in passage 14 on opposing sides of the catalyzed electrostaticsystem 22, although the housing 12 could have other numbers and types ofchambers in passage 14 in other configurations.

Referring to FIGS. 1-3, the corona discharge electrode device 20(1) islocated in the first chamber 26(1) in the passage 14 adjacent the inlet16, although other numbers and types of devices for charging particulatematter and in other locations could be used. The corona dischargeelectrode device 20(1) provides a corona discharge that is used tocharge particles in an exhaust stream passing through a chamber 26(1) inthe passage 14 in housing 12, such as soot in diesel exhaust.

The corona discharge electrode device 20(1) includes a ceramic base 30,a conductive rod 32, and a probe 34(1), although the corona dischargeelectrode device 20(1) could be comprised of other types and numbers ofelements in other configurations. The base 30 is formed around andinsulates the rod 32 and has a threaded end which is used to secure thebase 30 in an opening in the housing 12 so the probe 34(1) is disposedin the passage 14, although other types of bases made of other materialsand secured to the housing in other manners can be used and other typesof conductors can be used for rod 32. In these embodiments, the probe34(1) has an elongated, rectangular shape with teeth 35 that have sharppeaks along three sides and a smooth edge along the remaining side andthe probe has a twisted configuration, although the probe 34(1) couldhave other numbers and type of teeth along other numbers of edges andcould have other shapes in other configurations. Additionally, in thisembodiment the probe 34(1) is made of brass, although other types ofmaterials could be used.

By way of example only, other embodiments of probes 34(2)-34(4) whichcould be used with one or both of the corona discharge electrode devices20(1) and 20(2) are illustrated in FIGS. 6A-6C. In this embodiment, theprobe 34(2) has an elongated shape with a plurality of teeth 37 onopposing elongated sides, although the probe 34(2) could have othershapes and configurations. Each of the teeth 37 have: a sawtooth shape;substantially the same overall size; a spacing between each of the teeth37 which is substantially the same; and a direction in which each of theteeth 37 on the same elongated side extend in substantially the samedirection, although the probe 34(2) could have other types and numbersof teeth, with other spacing and direction, and with other shapes andconfigurations on other numbers of sides.

In this embodiment, the probe 34(3) has an elongated shape with aplurality of teeth 39 on opposing elongated sides and with an overalltwisted configuration, although the probe 34(3) could have other shapesand configurations. Each of the teeth 39 have: a sawtooth shape; anoverall size for each of the teeth 39 which tapers down from a centertowards each of the ends of the probe 34(3); a spacing between each ofthe teeth 39 which is substantially the same; and a direction in whicheach of the teeth 39 on the same elongated side extend in substantiallythe same direction, although the probe 34(3) could have other types andnumbers of teeth, with other spacing and direction, and with othershapes and configurations on other numbers of sides.

In this embodiment, the probe 34(4) has an elongated shape with aplurality of teeth 41 on opposing elongated sides, although the probe34(3) could have other shapes and configurations. Each of the teeth 41have: a sawtooth shape; substantially the same overall size; a spacingbetween each of the teeth 41 which is substantially the same; and adirection in which each of the teeth 41 on the same elongated sideextend varies between the teeth 41, although the probe 34(4) could haveother types and numbers of teeth, with other spacing and direction, andwith other shapes and configurations on other numbers of sides

The different shapes, configurations, sizes and directions for the teethon the probes 34(1)-34(4) improve the corona discharge from the coronadischarge electrode devices 20(1) and 20(2). Unlike prior single pole,mesh type, or plate electrodes which serve a limited area of exhaust gasflow, the use of corona discharge electrode devices 20(1) and 20(2) withone of these probes 34(1)-34(4) leads to the formation of widerectangular ionization field which covers a wide area of the passage 14in housing 12.

Referring to FIG. 1, the corona discharge electrode device 20(2) isidentical to the corona discharge electrode device 20(1) illustrated anddescribed with reference to FIGS. 1-3, except as described herein. Thecorona discharge electrode device 20(2) is located in the second chamber26(2) in the passage 14 between the catalyzed electrostatic system 22and the catalyst system 24, although other numbers and types ofdischarge devices could be used. The corona discharge electrode device20(2) provides a corona discharge in the chamber 26(2) in the passage 14downstream from the catalyzed electrostatic system 22. The coronadischarge is used to convert compounds in the exhaust stream, such asNO, to other compounds, such as NO₂, which can be treated by thecatalyst system 24.

A high voltage power source 28 is coupled to the corona dischargeelectrode devices 20(1) and 20(2) and supplies power at a very highvoltage between about 5 kV and 70 kV at a very low current between about0.01 mA and 7 mA, although the power supply 28 can supply power at othervoltages and currents to the corona discharge electrode device 20(1).One of the advantages of the present invention is that the system 10works effectively with the corona discharge electrode devices 20(1) and20(2) generating non-thermal plasma which requires less power and thusis more energy efficient.

Referring to FIGS. 1 and 4, the catalyzed electrostatic system 22comprises a substrate core 35 which has a plurality of passages 36 thatextend through, although the catalyzed electrostatic system 22 cancomprise other types and numbers of components in other configurationsand other types and numbers of attraction systems could be used. In thisembodiment, the substrate core 35 is made of a metal with a silvercoating in the passages 36, although the catalyzed electrostatic system22 can comprise other types and numbers of components in otherconfigurations and the substrate core and the coatings can be made ofother types of materials. The catalyzed electrostatic system 22 islocated in and fills the space in the passage 14 between the chambers26(1) and 26(2) which are fluidly connected together by the passages 36,although other configurations could be used. The conductive surfaces ofthe catalyzed electrostatic system 22 are coupled to ground, althoughother types of electrically connections could be used, such as couplingthe conductive surfaces of the catalyzed electrostatic system 22 to adevice with an opposite charge from the charge on the particles.

The catalyzed electrostatic system 22 uses an electrostatic principal todeflect and attract charged soot particles in the exhaust stream to asurface of one of the passages 36 in the substrate core 35, althoughother manners for attracting the particles on other types of surfacescan be used. Additionally, the catalyzed electrostatic system 22provides space for the conversion of soot and other particulatematerials captured on the catalyzed electrostatic system 22 throughoxidation so the catalyzed electrostatic system 22 can self regenerate.

Referring to FIG. 1, the catalyst system 24 includes a catalystsubstrate 38 with a plurality of passages 40 and is made of a ceramicmaterial, although the catalyst system 24 can comprise other types andnumbers of components in other configurations and can be constructedwith other types of materials. The catalyst system 24 is located in andfills the space of the passage 14 between the chamber 26(2) and theoutlet 18 which are fluidly coupled together, although otherconfigurations could be used. The catalyst system 24 is used to reduceor eliminate tailpipe emissions such as CO, HC and NOx with one or morereactions with catalysts in the catalyst system 24 in manners well knownto those of ordinary skill in the art.

A method of reducing emissions in accordance with embodiments of thepresent invention will now be described with reference to FIGS. 1-4. Anexhaust stream, such as diesel soot, is introduced through the inlet 16into the chamber 26(1) in the passage 14, although other types of fluidscould be introduced for treatment. Meanwhile, power supply 28 is engagedto supply power to the corona discharge electrode devices 20(1) and20(2) in manners well known to those of ordinary skill in the art. Inthese embodiments, the power supplied to corona discharge electrodedevices 20(1) and 20(2) is at very high voltage between about 5 kV and70 kV with a very low current between about 0.01 mA and 7 mA, althoughthe power can be supplied at other voltages and currents.

The high voltage applied to the corona discharge electrode device 20(1)charges carbon particles in the exhaust stream with ions repelled by thecorona discharge in chamber 26(1), although other manners for chargingthe particulate matter in chamber 26(1) can be used. The shape andconfiguration of the probe 34(1) on the corona discharge electrodedevice 20(1) leads to the formation of an ionization field which coversa substantial portion of the chamber 26(1). The corona discharge in thechamber 26(1) also excites the gas atoms to produce highly reactive O,OH, and NO₂ radicals. These highly reactive radicals oxidize at least aportion of the soot particles passing through chamber 26(1) into gases,such as N₂, CO, CO₂ and H₂O by way of example only.

Next, the charged particles in the exhaust stream in chamber 26(1) aredirected downstream into the passages 36 in the substrate core 35 ofcatalyzed electrostatic system 22, although the charge particles couldbe directed to other types of attraction systems. The charge particlesin the exhaust stream migrate to and are attracted on the conductivesurfaces in the passages 36 in the substrate core 35 which are coupledto ground G, although the conductive surfaces could be coupled in othermanners, such as to a device which provides an opposite charge from thecharge on the charge particles. By way of example only, particlemigration velocities of 0.01 to 4 ft/sec are common.

Meanwhile, the radicals, such as O, OH, and NO₂, generated in thechamber 26(1) are also directed downstream into the passages 36 in thesubstrate core 35 in catalyzed electrostatic system 22. The radicals,such as O, OH, and NO₂, also oxidize at least a portion of the particlesattracted on the conductive surfaces in the passages 36 in the substratecore 35 to self regenerate the catalyzed electrostatic system 22. Thesehighly reactive radicals oxidize the attracted particles into gases,such as N₂, CO, CO₂ and H₂O, while again self regenerating the catalyzedelectrostatic surface.

Next, the high voltage applied to the corona discharge electrode device20(2) generates a corona discharge in chamber 26(2), although othermanners for generating a corona discharge or other plasma can be used.The shape and configuration of the probe 34(1) on the corona dischargeelectrode device 20(2) helps to lead to the formation of the ionizationfield which covers a substantial portion of the chamber 26(2). Thecorona discharge in chamber 26(2) converts any residual compounds, suchas NO, in the exhaust stream from the catalyzed electrostatic system 22into other compounds, such as NO₂, which can be treated by the catalystsystem 24, although other manners for preparing the exhaust stream inchamber 26(2) for further treatment can also be used. Yet anotherfunction occurring in chamber 26(2) with the ionization is theoxidization of at least a portion of any remaining soot particles intogases, such as N₂, CO, CO₂ and H₂O

Next, the exhaust stream is provided into the passages 40 in thecatalyst substrate 38 for the catalyst system 24 to reduce or eliminatetailpipe emissions, such as CO, HC and NOx, with one or more reactionswith catalysts in the catalyst system 24 in manners well known to thoseof ordinary skill in the art. The treated exhaust stream is then outputvia the outlet 18 in the housing 12, although other treatments could beapplied and the exhaust could be outlet in other manners.

By way of example only, sample result from a diesel generator equippedwith the system 10 is shown in FIG. 5. As illustrated, the system 10providing a particulate matter reduction between about 37% and 80%depending upon the engine load and the level of power supplied by thepower supply 28 to the corona discharge electrode devices 20(1) and20(2). These results prove the feasibility of using non-thermal plasmawith the system 10 as a viable method to reduce soot in a dieselgenerator and diesel engine exhaust. Additionally, by way of exampleonly, the results from a diesel pick up truck equipped with the system10 are also illustrated in the table shown in FIG. 7.

The present invention has a number of applications, including as acomponent of an emissions treatment system for automotive applications,such as off-road vehicles, distributed power systems, stationary powersystems and mining systems. Other applications for the presentinvention, by way of example only, include removal of tar in biomassconversion and in stack gas applications.

Accordingly, the present invention provides a particulate trap systemwhich is effective in reducing emissions, is durable, and isself-regenerating. Since the present invention works with non-thermalplasma, it is very efficient in terms of power consumption when comparedto prior particle separation and trapping technologies. Anotheradvantage of the present invention is the simplicity and effectivenessof the design of the corona probe. Yet another advantage of the presentinvention is the absence of precious metal such as Platinum forconversion of NO to NO₂. Yet a further advantage of the presentinvention is that the low temperature (>=100° C.) operation of thesystem 10 makes it very suitable for use in vehicles and systems, suchas school busses, refuse trucks, construction equipment, on and off roadvehicles, and generators by way of example only.

Having thus described the basic concept of the invention, it will berather apparent to those skilled in the art that the foregoing detaileddisclosure is intended to be presented by way of example only, and isnot limiting. Various alterations, improvements, and modifications willoccur and are intended to those skilled in the art, though not expresslystated herein. These alterations, improvements, and modifications areintended to be suggested hereby, and are within the spirit and scope ofthe invention. Additionally, the recited order of processing elements orsequences, or the use of numbers, letters, or other designationstherefore, is not intended to limit the claimed processes to any orderexcept as may be specified in the claims. Accordingly, the invention islimited only by the following claims and equivalents thereto.

What is claimed is:
 1. A method for treating emissions, the methodcomprising: charging carbon particles in an exhaust stream in a housingwith a passage having an inlet and an outlet by a first corona dischargein a first chamber which generates a non-thermal plasma that charges thecarbon particles with ions from the first corona discharge; producingone or more radicals by exciting gas atoms in the exhaust stream by thefirst corona discharge; oxidizing a portion of the charged carbonparticles with a portion of the produced radicals to remove a portion ofthe carbon particles in the exhaust stream; attracting a portion of thecharged carbon particles in the exhaust stream on a flow-throughmaintenance-free attraction system comprising a substrate core having aplurality of individual passages that extend therethrough and whichfills a space in the housing passage that electrostatically attracts aportion of the charged carbon particles on a catalyzed attractionsurface oppositely charged from the charged carbon particles andgrounded; and oxidizing the attracted particles with another portion ofthe one or more produced radicals to self regenerate the at least oneattraction surface.
 2. The method as set forth in claim 1 wherein theproduced one or more radicals comprises at least one of O, OH, and NO₂.3. The method as set forth in claim 1 wherein the portion of removedcarbon particles are removed from the exhaust stream by the first coronadischarge device by being oxidized into gases comprising at least one ofN₂, CO, CO₂,and H₂O.
 4. The method as set forth in claim 1 wherein theattracted particles on the attraction surface are oxidized into gasescomprising at least one of N₂, CO, CO₂ and H₂O to self regenerate theattraction surface.
 5. The method as set forth in claim 1 furthercomprising: generating a second corona discharge in a second chamberwhich generates a non-thermal plasma that oxidizes a portion of thecharged carbon particles with ions from the second corona discharge andconverts residual compounds from the first chamber into other compoundswhich can be treated by a catalyst system; and catalyzing the othercompounds in a flow-through catalyst system comprising a substratehaving a plurality of individual passages that extend therethrough andwhich fills a space of the housing passage between the second chamberand the outlet to reduce or eliminate emissions from the exhaust stream.6. The method as set forth in claim 5 wherein the portion of chargedcarbon particles are removed from the exhaust stream by the secondcorona discharge device by being oxidized into gases comprising at leastone of N₂, CO, CO₂, and H₂O.
 7. The method as set forth in claim 5wherein the other catalyzed compounds reduced or eliminated from theexhaust stream are emissions comprising at least one of CO, HC, andNO_(x).
 8. The method as set forth in claim 5 wherein the second coronadischarge converts the residual compounds from the first coronadischarge into other compounds by converting at least a portion ofnitrogen oxide in the exhaust stream to nitrogen dioxide.